基于镜像和奇偶校验容许两个盘故障的磁盘阵列数据布局

通过讨论由数据条纹、其镜像和奇偶校验组成的校验条纹的容许两个盘故障的阵列布局,给出了一种新的阵列布局策略:把校验条纹的单元划分作为阵列布局的一个主要步骤,使得容许两个故障的条件通过校验条纹的单元划分来实现。为讨论容许多个盘故障的阵列布局提供了一条新途径。给出了校验条纹的容许两个故障的单元划分条件以及多种划分。对每个l(m+2l2m+1),利用给出的l—划分,设计了一种容许两个盘故障的阵列布局方案。给出的阵列布局方案具有高的可靠性、高的吞吐量、好的I/O性能以及简单的编码和解码算法。     

基于V码的高可靠性磁盘阵列容错模型

在磁盘阵列模型中，关键是如何实现容许多个磁盘阵列故障使得系统性能达到最优。该文提出了一类新的纠双错编码――V码，使用该编码的磁盘阵列数据布局，阵列的盘数可以为偶数，校验信息均匀分散在阵列每个盘中，容许任意2个磁盘故障。与其它纠双码的磁盘阵列布局进行比较，当阵列盘数为偶数时，V码阵列布局具有最优性能，编译码复杂度、冗余率达到最低以及小写性能最优，利于解决磁盘阵列I/O问题。     

一种基于3容错阵列码的RAID数据布局

在EVENODD码的基础上,提出一种新的基于EEOD码的RAID数据布局,只需要3个额外的磁盘保存校验信息,能容许任意3个磁盘同时故障,并给出了EEOD的代数定义,理论上证明了EEOD码的MDS性质.从一种新的途径讨论了EEOD码的译码过程:用图的回路表示通过"异或"运算得到的校验方程组,把译码过程归结为图回路的叠加,进而校验方程组图中度为偶数的顶点逐步消除.讨论了基于EEOD码阵列布局的性能,与其它RAID结构相比,容灾能力大幅度提高,编码和译码过程只需要简单的异或运算,但是空间利用率影响非常小,并且EEOD具有很好的性能,具有很好的应用前景.     

用双目标加权遗传算法解决网络磁盘阵列系统下校验散布布局优化问题的研究

廉价磁盘冗余阵列(RAID)作为一种提高存储系统可靠性和性能的技术,已经得到了广泛的应用,有关磁盘阵列结构和数据布局的研究也一直很活跃,但有关网络磁盘阵列下的数据布局的研究还不太多。本文首先概述了校验散布布局的技术和遗传算法的相关知识,提出了利用双目标加权遗传算法的思想解决网络磁盘阵列系统校验散布布局优化的问题。然后以“重构负截均匀分布”和“校验均匀分布”为双目标,使用改变的NSGA来解决网络磁盘阵列系统下校验散布布局的优化问题。最后给出了实验结果。     

磁盘阵列设计中几个问题的探讨

本文在简要介绍廉价冗余磁盘阵列的一些概念后，结合笔者研制ＤＡＳ３０００系列盘阵的实践，重点讨论了盘阵列设计中遇到的几个问题，包括对校验的计算与传输速度的关系、残缺恢复对系统性能的影响以及主轴同步是否必需等。文章认为，及时制定新的接口标准以及来自操作系统的支持．将直接影响到下一代ＲＡＩＤ的性能。     

基于LinuX系统的容双故障软磁盘阵列平台Deraid

提出并设计实现了一个基于Linux系统平台的容双故障的通用软磁盘阵列平台Deraid。它容许阵列中任意两个磁盘同时出错而保证数据不丢失,可以为各种需要大容量存储的系统提供容量大、吞吐量高的存储服务,同时具有良好的可扩展性,可为各种数据布局提供一个使用方便的实验平台。章讨论了Deraid的总体设计和实现的技术要点,并给出了具体的应用和性能测试结果。     

高可靠磁盘阵列的设计

可靠性是网络存储系统最重要的指标之一，冗余磁盘阵列(RAID)是网络存储系统的基础和关键部件，RAID一方面通过冗余数据或校验信息增强容错能力；另一方面通过硬件部件冗余来提高系统可靠性。重点研究提高RAID可靠性的关键技术。分析降低磁盘阵列可靠性的几种主要因素：系统故障、不可纠位错误和相关联的磁盘故障，研究相应的防御措施，对双重校验信息冗余技术、硬件部件冗余技术、快速故障盘重建等关键容错技术进行研究与探讨。     

异构磁盘阵列RAID5结构数据布局研究

由于应用需求的快速发展以及网络存储系统的出现,因此异构磁盘阵列的变得越来越常见。RAID5由于较高的性能和可靠性以及较低的代价,是应用最为广泛的RAID结构。目前对异构磁盘阵列RAID5结构的研究,重点主要放在充分利磁盘存储空间以及对性能的定性研究。论文提出了一种异构磁盘阵列RAID5结构数据布局优化方法,该方法充分考虑异构磁盘的相对容量和性能,以及校验单元的散布对RAID5小数据写性能的影响,可以生成负载均匀分布或接近均匀分布的布局。仿真实验结果表明,对于多用户小数据访问模式,优化布局的性能明显优于简单RAID5布局,且具有更高的伸缩性。     

基于奇偶校验的三容错数据布局研究

基于单容错编码的数据布局已经不能满足存储系统对可靠性越来越高的要求。对基于多容错编码的数据布局的研究受到了广泛的关注，并且出现了一些三容错的布局算法，如HDD1，HDD2等。但这些布局算法普遍存在冗余度较差、计算负载大等缺点。提出了一种基于三重奇偶校验的多容错数据布局算法TP-RAID(Triple Parity RAID)。该算法只需要在RAID5阵列系统中增加两个校验磁盘，通过水平、正向对角和反向对角三重奇偶校验，可容许同时发生的三个磁盘故障。该算法编码、解码简单，三重校验条纹长度相等，计算负载小，易于实现。此外，由于该算法中尽量减少了三重校验之间逻辑关联，使得该算法的小写性能比其他的三容错算法相比有了大幅度的提高。     

GC-RAIS:一种基于垃圾回收感知的固态盘阵列

垃圾回收操作会显著影响固态盘的性能,进而导致固态盘阵列的性能波动.为此,提出一种基于垃圾回收感知的磁盘阵列(GC-RAIS),充分利用固态盘的高随机读特性和固态盘阵列中的热备份盘,以减轻垃圾回收操作对固态盘阵列性能波动的负面影响.当固态盘阵列中某个固态盘正在处理垃圾回收操作时,对于到达该固态盘的读请求采用重构方式处理,即读取同一条带上其他固态盘上的数据重构得到,而对于到达该固态盘的写请求则将写数据临时存放在热备盘中,并更新相应的校验信息.当垃圾回收过程结束后,将被重定向的写数据写回到正确的固态盘中.仿真实验结果表明相对局部垃圾回收LGC策略和全局垃圾回收GGC策略,GC-RAIS分别减少用户I/O请求的平均响应时间达55％和25％.     

Reconstruct versus read-modify writes in RAID

RAID5 (Redundant Arrays of Independent Disk level 5) is a popular paradigm, which uses parity to protect against single disk failures. A major shortcoming of RAID5 is the small write penalty, i.e., the cost of updating parity when a data block is modified. Read-modify writes and reconstruct writes are alternative methods for updating small data and parity blocks. We use a queuing formulation to determine conditions under which one method outperforms the other. Our analysis shows that in the case of RAID6 and more generally disk arrays with k check disks tolerating k disk failures, RCW outperforms RMW for higher values of N and G. We note that clustered RAID and variable scope of parity protection methods favor reconstruct writes. A dynamic scheme to determine the more desirable policy based on the availability of appropriate cached blocks is proposed.     

X-code double parity array operation with two disk failures

X-code extends parity coding for correcting single disk failures in RAID 5 to two disks. Similar to RAID 6 X-code uses the minimum level of redundancy by dedicating the capacity of two out of N disks to check disks, but unlike RAID 6 it solely relies on parity codes, which are placed horizontally rather than vertically. The parity groups in X-code are defined as diagonals with positive and negative slopes. This study is mainly concerned with X-code arrays with two disk failures, since it requires a multistep recovery process, while its operation is otherwise similar to RAID 6. We use examples to gain insight into the cost of recovery and to develop an algorithm to estimate recovery cost for reconstructing two failed disks. We observe that disk loads are unbalanced and the overall load increase depends on the separation of the failed disks. Cyclically shifting or randomly permuting successive N×N arrays of blocks may be used to reduce the load increase to the mean across all of the possible (N−1)/2 distances of the failed disks. We also present an improvement in recovery cost for single disk failures.     

Efficient placement of parity and data to tolerate two diskfailures in disk array systems

In this paper, we deal with the data/parity placement problem which is described as follows: how to place data and parity evenly across disks in order to tolerate two disk failures, given the number of disks N and the redundancy rate p which represents the amount of disk spaces to store parity information. To begin with, we transform the data/parity placement problem into the problem of constructing an N×N matrix such that the matrix will correspond to a solution to the problem. The method to construct a matrix has been proposed and we have shown how our method works through several illustrative examples. It is also shown that any matrix constructed by our proposed method can be mapped into a solution to the placement problem if a certain condition holds between N and p where N is the number of disks and p is a redundancy rate     

Coding techniques for handling failures in large disk arrays

A crucial issue in the design of very large disk arrays is the protection of data against catastrophic disk failures. Although today single disks are highly reliable, when a disk array consists of 100 or 1000 disks, the probability that at least one disk will fail within a day or a week is high. In this paper we address the problem of designing erasure-correcting binary linear codes that protect against the loss of data caused by disk failures in large disk arrays. We describe how such codes can be used to encode data in disk arrays, and give a simple method for data reconstruction. We discuss important reliability and performance constraints of these codes, and show how these constraints relate to properties of the parity check matrices of the codes. In so doing, we transform code design problems into combinatorial problems. Using this combinatorial framework, we present codes and prove they are optimal with respect to various reliability and performance constraints.This paper is a revised and expanded version of material that appeared at the Third International Conference on Architectural Support for Programming Languages and Operating Systems (ASPLOS III), Boston, MA, March 1989. The work here was supported in part by the National Science Foundation under Grant Numbers MIP-8715235 and CCR-8411954, as well as an AT&T Bell Labs GRPW grant, a Siemens Corporation grant, and an IBM graduate fellowship.     

A multiple disk failure recovery scheme in RAID systems

In this paper, we propose a practical disk error recovery scheme tolerating multiple simultaneous disk failures in a typical RAID system, resulting in improvement in availability and reliability. The scheme is composed of the encoding and the decoding processes. The encoding process is defined by making one horizontal parity and a number of vertical parities. The decoding process is defined by a data recovering method for multiple disk failures including the parity disks. The proposed error recovery scheme is proven to correctly recover the original data for multiple simultaneous disk failures regardless of the positions of the failed disks. The proposed error recovery scheme only uses exclusive OR operations and simple arithmetic operations, which can be easily implemented on current RAID systems without hardware changes.     

构造高可靠性盘阵列结构的研究

本文比较分析了纠单错阵列与纠双错盘阵列的可靠性；指出若只考虑盘一级可靠性，纠双错阵列平均无故障时间（ＭＴＴＦ）是纠单错阵列的几千倍；介绍了一种新型的适用于阵列的纠双错编码——ＥＶＥＮＯＤＤ码，以及两种考虑阵列支撑硬件容错能力的阵列结构：正交结构和Ｃｒｏｓｓｈａｔｃｈ结构；指明将纠双错编码应用于正交结构或Ｃｒｏｓｓｈａｔｃｈ结构的盘阵列中，可大大提高阵列可靠性，并提出了一种应用现有单端口盘构造Ｃｒｏｓｓｈａｔｃｈ结构的方案     

磁盘阵列校验信息的放置策略

廉价磁盘冗余阵列（ＲＡＩＤ）采用许多小的廉价磁盘来代替大容量昂贵的磁盘，以取得更高的性能和更低的功耗。本文介绍了ＲＡＩＤ－５级磁盘阵列中校验信息的八种不同的分布策略，即奇偶校验信息的放置策略，并从几个不同的应用情况对不同的放置策略进行了研究，结论是不同的奇偶校验信息放置策略对磁盘阵列的Ｉ／Ｏ读写性能有很大的影响。     

Efficient parity placement schemes for tolerating up to two disk failures in disk arrays

In order to achieve high reliability in disk array systems, two new schemes using dual parity placement, called DH1 (diagonal–horizontal) and DH2 schemes, are presented. Both DH schemes can tolerate up to two disk failures by using two types of parity information placed in the diagonal and the horizontal directions, respectively, in a matrix of disk partitions. DH1 scheme can reduce the occurrences of the bottleneck problem significantly because the parity blocks are evenly distributed throughout the disk array. DH2 scheme uses one more disk than DH1 scheme in order to store the horizontal parities, while the diagonal parities are placed in the same way as in DH1 scheme with a minor change. Even though both DH schemes use almost optimal disk space for storing the redundant information, the encoding algorithms for them are quite simple and efficient. Moreover, both DH schemes can recover rapidly from any two disk failures.     

磁盘阵列设计中几个问题的探讨

本文在简要介绍廉价冗余磁盘阵列的一些概念后，结合笔者研制ＤＡＳ３０００系列盘阵的实践，重点讨论了盘阵设计中遇到的几个问题，包括对校验的计算与传输速度的关系、残缺恢复对系统性能的影响以及主轴同步是否必需等。文章认为，及时制定新的接口标准以及来自操作系统的支持，将直接影响到一下代ＲＡＩＤ的性能